1. Field of the Invention
This invention relates to an optical disk drive. More particularly, this invention relates to an optical disk drive for recording and reproducing information by the use of evanescent light.
2. Description of the Related Art
Innovative development and improvement have been made from various aspects in technologies for achieving a high recording density in the information recording field.
One of the high density recording technologies that has been proposed is a method that uses a lens capable of generating evanescent waves. This lens is referred to as a xe2x80x9csolid immersion lensxe2x80x9d. In a solid immersion lens, rays of light undergo total internal reflection and generate an evanescent wave. The evanescent wave generated by the solid immersion lens forms a very fine optical spot. Therefore, the solid immersion lens makes it possible to improve the information recording density on a recording medium such as an optical disk.
As illustrated in FIG. 11 of the accompanying drawings, an optical disc drive using the solid immersion lens comprises a fixed optical system 53 including a laser beam source 68, rise-up mirrors 56 for causing parallel rays of light to be incident vertically on a disk 51, and an evanescent optical system 60 for causing the parallel rays of light incident from above to generate evanescent waves and irradiating a very fine optical spot at a lower portion. Recording and reproduction of information to and from the disk 51 is executed by means of the very fine optical spot irradiated from the evanescent optical system 60.
Here, the term xe2x80x9crise-up mirror 56xe2x80x9d represents all those optical components which are equipped with a plane for reflecting the rays of light, and is inclusive of a beam splitter. The evanescent optical system 60 is an optical element containing the solid immersion lens 65 described above.
The need to reduce the thickness of various devices related to personal computers has become greater in recent years as personal computers have been rendered xe2x80x9cmobilexe2x80x9d.
In the construction depicted in FIG. 11, however, both evanescent optical system 60 and rise-up mirror 56 are disposed on the disk plane side for recording or reproducing the information. In other words, a space corresponding to the height of at least these two optical elements is necessary on one of the surface sides of the disk.
When an optical disk drive can record or reproduce information on at least two disk surfaces on the basis of the construction shown in FIG. 11, the space corresponding to the height of the two optical elements must be secured on each disk surface with the result that the total thickness of the optical disk drive increases.
In view of the problem described above, the present invention is directed to provide an optical disk drive that can restrict the increase of the thickness of the apparatus particularly when the information is recorded or reproduced on at least two disk surfaces.
To accomplish the object described above, the present invention provides an optical disk drive as described below.
In a first aspect of the invention, an optical disk drive comprises an optical disk which permits transmission of a laser beam, an optical disk holding mechanism configured to rotatably support the optical disk, a first laser beam irradiation mechanism disposed on one side of the optical disk, configured to cause the first laser beam to be incident vertically on one surface of the optical disk, and a first evanescent optical system disposed on the other side of the optical disk, configured to receive a first laser beam which emanates from the laser beam irradiation mechanism and passes through the optical disk, and configured to radiate the first evanescent wave to the other surface of the optical disk having at least one recording surface.
Embodiments of this aspect of the present invention may have any of the following features:
(1) A track pitch of a signal train recorded to the optical disk may be smaller than the wavelength of the first laser beam.
(2) The first laser beam irradiation mechanism may have a first mirror disposed at a position opposing the first evanescent optical system.
(3) The first mirror may be a 45xc2x0 mirror.
(4) The first mirror may be a prism.
(5) The first evanescent optical system may include a first solid immersion lens.
(6) The first solid immersion lens may include a bottom surface to which the first laser beam is incident and which radiates the first evanescent wave, and a reflecting surface which reflects the first laser beam incident from the lens bottom surface and converges the first laser beam to the lens bottom surface.
(7) The distance between the lens bottom surface of the first solid immersion leans and the surface of the optical disk opposing the lens bottom surface may be within the attenuation distance of the evanescent wave.
(8) The optical disk drive may further comprise a second laser beam irradiation mechanism disposed adjacent to the first evanescent optical system, configured to cause the second laser beam to be vertically incident to the other surface of the optical disk, and a second evanescent optical system disposed adjacent to the first laser beam irradiation mechanism, configured to receive the second laser beam incident from the second laser beam irradiation mechanism, passing through the optical disk, and configured to radiate the second evanescent wave to one surface of the optical disk.
(9) The optical disk holding mechanism may hold two or more optical disks.
In a second aspect of the invention, an optical disk drive comprises two optical disks which transmit laser beams, disposed at upper and lower positions, a first laser beam irradiation mechanism disposed on the upper surface side of the optical disk at the upper position, and used for recording or reproducing information on the lower surface of the optical disk at the lower position, a first evanescent optical system configured to receive the first laser beam irradiated from the first laser beam irradiation mechanism and pass through the two optical disks, and configured to radiate the first evanescent beam to the lower surface of the optical disk at the lower position, a second laser beam irradiation mechanism disposed on the lower surface side of the optical disk at the lower position, and used for recording or reproducing information on the upper surface of the optical disk held at the lower position, a second evanescent optical system configured to receive the second laser beam irradiated from the second laser beam irradiation mechanism, passing through the optical disk at the lower position, and configured to radiate the second evanescent beam to the upper surface of the optical disk held at the lower position, a third laser beam irradiation mechanism disposed on the upper surface side of the optical disk at the upper position, and used for recording or reproducing information on the lower surface of the optical disk at the upper position, a third evanescent optical system configured to receive the third laser beam irradiated from the third laser beam irradiation mechanism, passing through the optical disk at the upper position, and configured to radiate the third evanescent beam to the lower surface of the optical disk at the upper position, a fourth laser beam irradiation mechanism disposed on the lower surface side of the optical disk at the lower position, and used for recording or reproducing information on the upper surface of the optical disk at the upper position, and a fourth evanescent optical system configured to receive the fourth laser beam irradiated from the fourth laser beam irradiation mechanism, passing through the two optical disks, and configured to radiate the fourth evanescent beams to the upper surface of the optical disk at the upper position.
Embodiments of this aspect of the present invention may have any of the following features:
(1) The first to fourth evanescent optical systems may include first to fourth solid immersion lenses.
(2) The first to fourth solid immersion lenses may include a lens bottom surface to which the first to fourth laser beams incident and which radiates the first to fourth evanescent waves, and reflecting surfaces for reflecting the first to fourth laser beams incident from the lens bottom surfaces and converging them on the lens bottom surfaces.
In the present invention, the two optical elements, i.e., the parallel beam irradiation mechanism and the evanescent optical system, can be separated from each other so as to interpose the optical disk not having an optical reflecting layer between them. Therefore, the present invention can improve freedom of disposition of these optical elements and will be able to restrict the thickness of the optical disk drive. Particularly when both surfaces of the optical disk are used for the recording surface or when a plurality of optical disks are used simultaneously the present invention provides a remarkable effect for restricting the thickness of the optical disk drive.